Methanol-Facilitated Cascaded Polyolefin Upcycling Enabling the Efficient Generation of High-Value C9+ Alkylaromatics.

Existing polyolefin chemical recycling and upcycling strategies predominantly yield fuels, waxes, and olefins, which are characterized by relatively low economic value. Although attempts have been made to synthesize functionalized chemicals, a particularly promising product category-C9-C12 polysubstituted alkylbenzenes with a market price exceeding 1400 USD per ton-remains largely overlooked. Herein, we present a novel methodology that utilizes methanol as a coreactant, with the goal of achieving high-yield synthesis of polysubstituted alkylbenzenes. Under mild reaction conditions (280 °C), the process attains a 97.8% conversion rate of low-density polyethylene (LDPE, Mw = 300 kDa) and complete conversion of methanol. Based on the mass of polyethylene, it produces 37 wt% of aromatic products, accompanied by an 87% increase in the mass yield of C9-C12 alkylbenzenes. Isotope-labeling experiments conducted with 13CH3OH and in situ FTIR disclose that methanol acts synergistically to promote carbocation-mediated C─C bond cleavage and self-amplifying Friedel-Crafts alkylation reactions. This mechanism steers the methylative homologation pathway toward the formation of polymethylated aromatics. The versatility of this approach, which is applicable to a wide variety of polyolefins, holds the promise of opening new pathways for a profitable circular economy in the plastics industry.